Astocker put 57 boxes of detergent on the shelves in 2 minutes. after 5 minutes, he had put 117 boxes on the shelves. how many boxes were on the shelves when he started?

57 boxes of detergent on the shelves in 2 minutes
After 5 minutes, he had put 117 boxes on the shelves

117 - 57 = 60 (60 boxes of detergent for 3 minutes)
60/3 = 20 (20 boxes of detergent per minute)
so

20 x 5 = 100 boxes of detergent 

117 - 100 = 17 boxes

answer
17 boxes of detergent were on the shelves when he started

(2,57)(5,117)
slope = (117 - 57) / (5 - 2) = 60/3 = 20

y = mx + b
slope(m) = 20
(2,57)...x = 2 and y = 57
sub and find b, the y int
57 = 20(2) + b
57 = 40 + b
57 - 40 = b
17 = b

equation is : y = 20x + 17with x being the number of minutes, and 17 being the number of boxes on the shelf when he started